Miniature electrochemical cell having a casing of a conductive plate closing an open-ended ceramic container having a via hole supporting a platinum-containing conductive pathway

ABSTRACT

A miniature electrochemical cell having a volume of less than 0.5 cc is described. The cell casing comprises an open-ended ceramic container having a via hole providing an electrically conductive pathway extending through the container. A metal lid closes the open-end of the container. An electrode assembly housed inside the casing comprises an anode current collector deposited on an inner surface of the ceramic container in contact with the electrically conductive pathway in the via hole. An anode active material contacts the current collector and a cathode active material contacts the metal lid. A separator is disposed between the anode and cathode active materials. That way, the electrically conductive pathway serves as a negative terminal, and the lid, electrically isolated from the conductive pathway by the ceramic container, serves as a positive terminal. The negative and positive terminals are configured for electrical connection to a load.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to the conversion of chemical energy toelectrical energy. More particularly, the present invention relates toan electrochemical cell that preferably has a total size or volume thatis less than 0.5 cc. Such so-called miniaturized electrochemical cellsenable numerous new and improved medical device therapies. Miniatureelectrochemical cells are defined as those having a size or total volumethat is less than 0.5 cc.

2. Prior Art

Electrochemical cells must have two opposite polarity terminals that areelectrically isolated from each other. In use, the terminals areconnected to a load, such as the circuitry of an implantable medicaldevice to power the medical device. In that respect, an electrochemicalcell which is sufficiently hermetic to prevent ingress of moisture andegress of electrolyte so that it can operate for ten years or morerequires robust sealing methodologies while still providing adequateelectrical isolation between the opposite polarity terminals. However,conventional sealing techniques are often not practical when cell sizedrops below 0.5 cc. That is because the seals themselves take up a majorportion of the overall cell volume.

For that reason, the present invention provides a casing constructionthat is suitable for use with both hermetically sealed primary andsecondary or re-chargeable electrochemical cells. While useful withcells of virtually any size, the present hermetic casing is particularlywell suited for cells having a total volume or size that is less than0.5 cc.

SUMMARY OF THE INVENTION

The present invention describes an electrochemical cell that is enabledby a casing construction which is readily adapted to miniature celldesigns. However, while the present casing is adapted for miniatureelectrochemical systems, the casing design is also applicable to cellsthat are not classified as “miniature”. A miniature electrochemical cellis defined as one having a total volume that is less than 0.5 cc.

A known problem with conventional miniature electrochemical cell designsis the need for the materials from which the cell is constructed to beboth chemically compatible with each other and not susceptible toundesirable corrosion reactions. A miniature electrochemical cellaccording to the present invention uses an electrically conductivemetal-containing paste that is filled into a via hole extending througha cup-shaped, open-ended ceramic container. The via hole is formed(drilled, punched or cut) with the ceramic container being in a greenstate. The open-ended ceramic container is then sintered to transformthe metal-containing paste into a solid electrically conductive pathwayextending through the sintered ceramic container.

Next, an anode current collector is deposited on an inner surface of theopen-ended ceramic container in contact with the electrically conductivepathway. In addition to providing electrical conduction from theto-be-deposited anode active layer to the electrically conductivematerial residing in the via hole, the anode current collector protectsthe metallic electrically conductive material from corrosive reactionswith other battery components while exhibiting good adhesion to theceramic container or, should there be one, to an adhesion layer, forexample an adhesion layer of titanium, on an inner surface of theceramic container. An exemplary anode current collector according to thepresent invention is from about 0.1 microns to about 50 microns thickand is comprised of a metallic layer deposited on the inner surface ofthe ceramic container using a physical vapor deposition (PVD) process,for example sputtering deposition or evaporation deposition, so that thedeposited metal serving as the current collector covers the via hole.Exemplary current collector materials include nickel, titanium, copper,and Ti/NiV composites.

An anode active material is deposited on the current collector oppositethe electrically conductive pathway. The anode active material ispressed into a pellet, spray-coated, or printed and has a shape thatencases the anode current collector to contact the inner surface of theceramic container. That way, the anode active material is in electricalcontinuity with the electrically conductive pathway through the currentcollector. The electrically conductive pathway serves as the negativeterminal for the electrochemical cell.

A separator is supported on the anode active material opposite theelectrically conductive material in the anode via hole. A cathode activematerial contacts the separator opposite the anode active material. Justbefore the open end of the ceramic container is closed with anelectrically conductive cover plate or lid, a nonaqueous electrolyte isfilled into the container. The electrolyte serves to activate theelectrode assembly comprising the anode and cathode active materialsprevented from direct physical contact with each other by theintermediate separator.

An intermediate ring-shaped gold pre-form resides between theelectrically conductive lid and the upper edge of an annular sidewallcomprising the open-ended ceramic container. Alternatively, a physicalvapor deposition (PVD) process is used to coat gold onto the upper edgeof the annular sidewall or onto an inner surface of the titanium lid.Preferably, the upper annular edge of the container is metallized priorto contacting the gold to the container. Then, an ultra-sonic weldingprocess or a laser welding process is used to melt and seal the gold tothe metal lid and to the ceramic container, thereby closing the open endof the container. An important aspect of the present miniatureelectrochemical cell is that the cathode active material directlycontacts an inner surface of the lid. That way, the lid serves as thepositive terminal for the electrochemical cell.

Thus, the present invention describes a miniature electrochemical cellactivated with a nonaqueous electrolyte. The anode or negative terminalis comprised of a metal-containing material residing in and hermeticallybonded or sealed to an anode via hole extending through the cup-shapedceramic container. The hermetic bond is formed by co-firing ametal-containing paste filled into the via hole extending through agreen ceramic body comprising the ceramic container. Themetal-containing material is preferably substantially pure platinum, ora platinum/ceramic composite and the open-ended ceramic container iscomprised of 3% YSZ or alumina. The metal lid is sized and shaped(configured) to close the open end of the ceramic container to therebyprovide the cell casing. The cathode active material contacts the lidand the separator opposite the anode active material.

Alternatively, the metal-containing material in the anode via hole isgold, which is formed by brazing gold into a via hole formed (drilling,punching, cutting, machining, and waterjet cutting) through thepre-sintered ceramic container. Prior to sintering the green-stateceramic container, the via hole is coated with titanium or titanium andniobium to facilitate gold wetting of the via hole wall.

The present electrochemical cell is not limited to any one chemistry andcan be of an alkaline cell, a primary lithium cell, a rechargeablelithium cell, a Ni/cadmium cell, a Ni/metal hydride cell, asupercapacitor, a thin film solid-state cell, and the like. Preferably,the cell is a lithium-ion electrochemical cell comprising a carbon-basedor Li₄Ti₅O₁₂-based anode and a lithiated metal oxide-based cathode, suchas of LiCoO₂ or lithium nickel manganese cobalt oxide(LiNi_(a)Mn_(b)Co_(1-a-b)O₂). In an alternate embodiment, the cell is ofa primary chemistry having a lithium anode and a metal oxide cathode,for example a silver vanadium oxide cathode active material. Fluorinatecarbon (CF_(x)) is another suitable cathode active material.

These and other aspects of the present invention will becomeincreasingly more apparent to those of ordinary skill in the art byreference to the following description and the appended drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view of one embodiment of a miniatureelectrochemical cell 10 according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A miniature cell according to the present invention is not limited toany one electrochemical system or chemistry. The miniatureelectrochemical cell can be an alkaline cell, a primary lithium cell, arechargeable lithium cell, a Ni/cadmium cell, a Ni/metal hydride cell, asupercapacitor, a thin film solid-state cell, and the like. An exemplaryminiature electrochemical cell is of a lithium-ion chemistry having acarbon-based anode and a metal oxide-based cathode, such as a cathode ofLiCoO₂ or LiNi_(a)Mn_(b)Co_(1-a-b)O₂ activated with a liquidelectrolyte.

Referring now to the drawing, FIG. 1 illustrates an exemplary embodimentof a miniature electrochemical cell 10 according to the presentinvention. The cell 10 has a casing comprising an open-ended container12 of an electrically insulative ceramic material. The container 12comprises a base 14 supporting an outwardly extending annular sidewall16. The annular sidewall 16 extends to an annular edge 18 spaced fromthe base 14. Preferably the sidewall 16 meets the base 14 at a rightangle.

The ceramic container 12 is comprised of 3% YSZ or essentially highpurity alumina ceramic of the chemical formula Al₂O₃. “Essentially pure”means that the post-sintered ceramic is at least 96% alumina up to99.999% alumina. In various embodiments, the post-sintered ceramiccontainer 12 is at least 90% alumina, preferably at least 92% alumina,more preferably at least 94% alumina, and still more preferably at least96% alumina.

The design of the container 12 is not limited to any one shape. As thoseskilled in the art will readily recognize, a myriad of different shapesis contemplated for the open-ended container 12, the specific shapebeing limited only by the form factor for the application or device thatthe cell 10 is intended to power. In that respect, a cross-section ofthe annular sidewall 16 has the same shape as the periphery of the base14.

The base 14 of the electrically insulative ceramic container 12 isprovided with a via hole 20 that extends to a base inner surface 22 anda base outer surface 24. The via hole 20 is preferably formed bydrilling, punching, cutting, machining, and waterjet cutting through theceramic.

A platinum-containing material, for example a substantially closed pore,fritless and substantially pure platinum material 26, fills the via hole20 to thereby form an electrically conductive pathway extending betweenand to the inner and outer surfaces 22, 24 of the ceramic base 14 of theopen-ended container 12. The platinum-containing material 26 ishermetically sealed to the ceramic base 14 and has a leak rate that isnot greater than 1×10⁻⁷ std. cc He/sec.

According to another embodiment of the present invention, in lieu of thesubstantially pure platinum material 26, the via hole 20 is filled witha composite reinforced metal ceramic (CRMC) material 28. The CRMCmaterial 28 is a platinum-containing material that comprises, by weight%, from about 10:90 ceramic:platinum to about 90:10 ceramic:platinum or,from about 70:30 ceramic:platinum to about 30:70 ceramic:platinum.

Examples of suitable CRMC materials 28 include, but are not limited to:

a) Alumina (Al₂O₃) or zirconia (ZrO₂) including various stabilized orpartially stabilized zirconia like zirconia toughened alumina (ZTA) andalumina toughened zirconia (ATZ) with platinum (Pt) or palladium (Pd);and

b) Alumina (Al₂O₃) or zirconia (ZrO₂) with iridium, rhenium, rhodium,various Pt alloys (e.g., Pt—Ir, Pt—Pd, Pt—Rh, Pt—Re, Pt—Au, Pt—Ag etc.),Pd alloys (e.g., Pd—Ir, Pd—Re, Pd—Rh, Pd—Ag, Pd—Au, Pd—Pt, Pd—Nb, etc.),Au alloys (e.g., Au—Nb, Au—Ti, etc.), Au alloys (e.g., Au—Nb, Au—Ti,etc.), and Ti alloys (e.g., Ti—Al—V, Ti—Pt, Ti—Nb, etc.).

Other non-limiting biocompatible metals and alloys that may be used inplace of platinum include niobium, platinum/palladium, stainless steels,and titanium.

Furthermore, any of the following materials may be used alone or incombination with any of the materials already discussed or within thislist: gold (Au), silver (Ag), iridium (Ir), rhenium (Re), rhodium (Rh),titanium (Ti), tantalum (Ta), tungsten (W), zirconium (Zr), and vanadium(V); cobalt chromium molybdenum alloy, cobalt chromium nickel ironmolybdenum manganese alloy, cobalt chromium tungsten nickel ironmanganese alloy, cobalt nickel chromium iron molybdenum titanium alloy,cobalt nickel chromium iron molybdenum tungsten titanium alloy, cobaltnickel chromium molybdenum alloy, copper aluminum nickel alloy, copperzinc alloy, copper zinc aluminum nickel alloy, copper zinc silver alloy,gold platinum palladium silver indium alloy, iron chromium alloy, ironchromium nickel alloy, iron chromium nickel aluminum alloy, ironchromium nickel copper alloy, iron chromium nickel copper molybdenumniobium alloy, iron chromium nickel copper niobium alloy, iron chromiumnickel copper titanium niobium alloy, iron chromium nickel manganesemolybdenum alloy, iron chromium nickel molybdenum alloy, iron chromiumnickel molybdenum aluminum alloy, iron chromium nickel titaniummolybdenum alloy, iron manganese chromium molybdenum nitrogen alloy,nickel platinum alloy, nitinol, nickel titanium alloy, nickel titaniumaluminum alloy, niobium-titanium alloy, platinum iridium alloy, platinumpalladium gold alloy, titanium aluminum vanadium alloy, titanium basedaluminum iron alloy, titanium based aluminum molybdenum zirconium alloy,titanium based molybdenum niobium alloy, titanium based molybdenumzirconium iron alloy, titanium based niobium zirconium alloy, titaniumbased niobium zirconium tantalum alloy, titanium molybdenum alloy,titanium niobium alloy, titanium platinum alloy, and titanium-basedmolybdenum zirconium tin alloy.

The interfacial boundary between the ceramic base 14 and thesubstantially pure platinum-containing material 26 or CRMC material 28forms a meandering or undulating path of sufficient tortuousity so thatthe boundary inhibits crack initiation, and more importantly, crackpropagation, and additionally, because of the intimacy of the interface,impairs leakage of fluids. As used herein, the word tortuous ortortuousity refers to the roughened, complex, or undulating interfacethat is formed at the boundary between the ceramic base 14 and thesubstantially pure platinum-containing material 26 or the CRMC material28. This tortuous interface is characterized by hills and valleys whichare topographically three dimensional and form very strong and reliablehermetic bonds.

In an exemplary embodiment of the present invention, a method ofmanufacturing the open-ended container 12 comprising the electricallyconductive pathway 26 or 28 includes forming the base 14 supporting theoutwardly extending annular sidewall 16 having the desired form factor,the container 12 being in a green state and comprising at least 96%alumina; forming the via hole 20 extending through the ceramic base 14;filling the via hole 20 with an electrically conductive paste (notshown), the electrically conductive paste comprising a mixture of asubstantially pure platinum powder, an inactive organic binder, andpossibly a solvent and/or plasticizer, or a CRMC powder and an inactiveorganic binder, solvent and/or plasticizer; placing the green-stateceramic container 12 and conductive paste filled via hole 20 into an airfilled heating chamber and heating the assembly to form a sinteredmonolithic structure. It is believed that the resulting substantiallypure platinum-containing material 26 forms an interface with the ceramiccontainer 12 comprising a glass that is at least about 60% silica.

It is understood that throughout this disclosure when substantially pureplatinum and CRMC pastes are referred to, those pastes include solventsand binders that are baked out during sintering. Suitable binders areselected from the group consisting of ethyl cellulose, acrylic resin,polyvinyl alcohol, polyvinyl butyral and a poly(alkylene carbonate)having the general formula R—O—C(═O)—O with R═C₁ to C₅. Poly(ethylenecarbonate) or polypropylene carbonate) are preferred poly(alkylenecarbonates). Suitable solvents are selected from the group consisting ofterpineol, butyl carbitol, cyclohexanone, n-octyl alcohol, ethyleneglycol, glycerol, water, and mixtures thereof.

In another exemplary embodiment, forming the ceramic container 12comprises laminating a plurality of ceramic green sheets together tothereby provide the desired form factor, followed by sintering.

In greater detail, to achieve sustainable hermeticity between theplatinum-containing material 26 and the ceramic base 14, the followingis required. Because the coefficient of thermal expansion (CTE) ofplatinum is sufficiently higher than the CTE of alumina, it is nottheoretically possible for alumina to provide compressive forces on asolid platinum body, for example a solid platinum wire, residing in avia hole extending through the alumina. To overcome the CTE differencesbetween these two materials, a platinum body residing in an alumina viahole must be formed using a platinum paste having a minimum of 80%platinum solids loading. The term “paste” is defined as a smooth, softmass having a pliable consistency and comprising pure platinumparticles, a binder material and a solvent. In a preferred embodiment,the solids loading of platinum particles in the paste is about 90%. In amore preferred embodiment, the solids loading of platinum particles inthe paste is about 95%.

In addition, the via hole 20 must be packed so that theplatinum-containing paste occupies at least about 90% of its availablespace. In a preferred embodiment, the platinum-containing paste occupiesabout 95% of the via hole space. In a more preferred embodiment, theplatinum-containing paste occupies about 99% of the via hole 20.

The shrinkage of the alumina must not be greater than about 20% of thatof the volume of the platinum-containing paste in the via hole 20. In apreferred embodiment, shrinkage of the alumina is about 14% of thevolume of the platinum-containing paste in the via hole 20. In a morepreferred embodiment, shrinkage of the alumina is about 16% of thevolume of the platinum-containing paste in the via hole 20.

After the platinum-containing paste is filled into the via hole 20extending through the ceramic base 14, the open-ended ceramic container12 is exposed to a controlled co-firing heating profile in ambient airthat comprises a binder bake-out portion, a sinter portion, and a cooldown portion.

In one embodiment, the binder bake-out portion of the controlledco-firing heating profile is performed at a temperature of from about400° C. to about 700° C. for a minimum of about 4 hours. A preferredbinder bake-out protocol is performed at a temperature of from about550° C. to about 650° C. A more preferred binder bake-out is performedat a temperature of from about 500° C. to about 600° C.

Next, the sintering portion of the controlled co-firing heating profileis preferably performed at a temperature ranging from about 1,400° C. toabout 1,900° C. for up to about 6 hours. A preferred sintering profileis at a temperature from about 1,500° C. to about 1,800° C. A morepreferred sintering temperature is from about 1,600° C. to about 1,700°C.

Then, the cool down portion of the controlled co-firing heating profileoccurs either by turning off the heating chamber and allowing thechamber to equalize to room temperature or, preferably by setting thecool down portion at a rate of up to about 5° C./min from the holdtemperature cooled down to about 1,000° C. At about 1,000° C., thechamber naturally equalizes to room temperature. A more preferred cooldown is at a rate of about 1° C./min from the hold temperature to about1,000° C. and then allowing the heating chamber to naturally equalize toroom temperature. In so doing, a robust hermetic seal is achievedbetween the mating materials of the ceramic container 12 and theplatinum-containing material 26 in the via hole 20.

During processing, compression is imparted by the ceramic base 14 aroundthe platinum-containing paste in the via hole 20 due to volume shrinkageof the alumina being greater than that of the paste. Furthermore, theplatinum is sufficiently malleable at this phase to favorably deform bythe compressive forces applied by the ceramic base 14. The combinationof the platinum solids loading in the paste, the platinum packing in thevia hole 20 and the shrinkage of the ceramic base 14 being greater thanthat of the platinum-containing paste as the paste is solidified to asolid platinum-containing material results in the platinum taking theshape of the mating alumina surface. The amount of platinum solidsloading, its packing percentage in the via hole 20 and the malleabilityof the platinum material all contribute to formation of a hermetic sealbetween the platinum-containing material 26 and the ceramic base 14. Inaddition, the compressive forces that result from the greater volumetricshrinkage of the ceramic base 14 than that of the platinum-containingmaterial 26 in the via hole 20 limit expansion of the platinum and forcethe platinum to deform to the contour of the surface of the via hole 20to consequently form a hermetic seal. Thus, an interface between theceramic base 14 and the platinum-containing material 26 that conforms tothe respective interface surfaces and results in a nearly exact mirrorimage of the interfacing surfaces is formed, thereby creating a hermeticbond therebetween.

Analysis of the interface between the ceramic base 14 and theplatinum-containing material 26 of this invention showed not only thecreation of an intimate interface, but, in the case of the interfaciallayer, a hermetic structure that exhibits an amorphous layer at theinterface comprising the elements platinum, aluminum, carbon and oxygenthat appear to impart resistance to erosion by body fluids. Both thesebonding mechanisms, direct bonding and an amorphous interfacial layer,offer additional tolerance to the CTE mismatch between the ceramic base14 and the platinum-containing material 26.

On the other hand, CRMC very closely matches the CTE of the alumina.This results in a very good hermetic seal between the CRMC and theceramic container 12. Under certain processing conditions cermets mayform a thin glass layer or even an alumina layer over the via ends. Inthat case, it may be necessary to perform an additional manufacturingstep, such as acid etch, lapping or mechanical abrasion, to remove thisformed layer.

While the above description regarding the controlled co-firing heatingprofile has been presented with respect to an alumina ceramic, it isbelieved that 3% YSZ ceramic will function in a similar manner.

For additional information regarding via holes filled with electricallyconductive materials, reference is made to U.S. Pat. No. 8,653,384 toTang et al., U.S. Pat. No. 9,492,659 to Tang et al., U.S. Pat. No.10,249,415 to Seitz et al. and RE47,624 to Tang et al. (which is are-issue of the '384 patent). These patents are assigned to the assigneeof the present invention and incorporated herein by reference. Foradditional information regarding via holes filled with a CRMC material,reference is made to U.S. Pat. No. 10,350,421 to Seitz et al. and U.S.Pat. No. 10,272,252 to Seitz et al. These patents are assigned to theassignee of the present invention and incorporated herein by reference.

Alternatively, the metal-containing material in the via hole 20 is gold.After sintering the green-state ceramic container and after the via holeis metallized with titanium or titanium and niobium to facilitate goldwetting of the via hole wall, a gold pre-form is positioned in the viahole 20. The ceramic container 12 is heated to melt the gold and bond itto the side walls of the metallized via hole.

After the open-ended ceramic container 12 with the platinum-containingmaterial 26 or 28 or gold residing in the via hole 20 is made, athin-film anode current collector 30 is contacted to the inner surface22 of the ceramic base 14 using physical vapor deposition (PVD). Theanode current collector 30 is preferably a continuous layer of nickeldevoid of perforations. The nickel current collector 30 has a thicknessmeasured outwardly from the inner surface 22 of the ceramic base 14 thatranges from about 0.1 μm to about 3 μm. Titanium, stainless steel,tantalum, platinum, gold, aluminum, cobalt, molybdenum, a Ti/NiVcomposite, and alloys thereof are also suitable materials for the anodecurrent collector 30.

A layer of anode active material 32 is supported on the anode currentcollector 30. The anode active material 32 preferably extends outwardlybeyond the peripheral edge of the current collector 30 to contact theinner surface 22 of the ceramic container. In that respect, the anodeactive material 32 is itself a shallow cup-shaped structure. The anodeactive material 40 has a thickness that ranges from about 25 μm to about4,000 μm. Suitable anode active materials include lithium and its alloysand intermetallic compounds including, for example, Li—Si, Li—Sn, Li—Al,Li—B and Li—Si—B alloys, and mixtures and oxides thereof.

When gold resides in the via hole 20 as the electrically conductivepathway, a current collector is not needed between the gold in the viahole and the anode active material 40. Instead, the anode activematerial 40 can contact the gold directly.

A separator 34 is positioned on top of the anode active material 32. Theseparator 34 preferably extends outwardly beyond the peripheral edge ofthe anode active material 32 and has a thickness that ranges from about5 μm to about 30 μm. Illustrative separator materials include non-wovenglass, polypropylene, polyethylene, microporous material, glass fibermaterials, ceramics, polytetrafluorethylene membrane commerciallyavailable under the designations ZITEX (Chemplast Inc.), polypropylenemembrane, commercially available under the designation CELGARD (CelanesePlastic Company Inc.) and DEXIGLAS (C. H. Dexter, Div., Dexter Corp.).Other separator materials that are useful with the present inventioninclude woven fabrics comprising halogenated polymeric fibers, asdescribed in U.S. Pat. No. 5,415,959 to Pyszczek et al., which isassigned to the assignee of the present invention and incorporatedherein by reference. Examples of halogenated polymeric materials thatare suitable for the present invention include, but are not limited to,polyethylene tetrafluoroethylene which is commercially available underthe name Tefzel, a trademark of the DuPont Company;polyethylenechlorotrifluoroethylene which is commercially availableunder the name Halar, a trademark of the Allied Chemical Company, andpolyvinylidene fluoride.

A layer of cathode active material 36 contacts the separator 34 oppositethe anode active material 32. In that respect, the separator 34physically segregates the cathode active material 36 from the anodeactive material 32 contacting the anode current collector 30. Thecathode active material 36 has a thickness that ranges from about 25 μmto about 5,000 μm.

The open end of the ceramic container 12 is closed with an electricallyconductive metal cover plate or lid 38, for example, a titanium lid. Thelid 38 is sized and shaped so that its outer annular edge 40 issubstantially aligned with the outer surface of the container sidewall16.

However, prior to closing the open end of the ceramic container 12 withthe lid 38, a nonaqueous, ionically conductive electrolyte (not shown)having an inorganic, ionically conductive salt dissolved in a nonaqueoussolvent and, more preferably, a lithium salt dissolved in a mixture of alow viscosity solvent and a high permittivity solvent is filled into theceramic container 12. The salt serves as the vehicle for migration ofthe anode ions to intercalate or react with the cathode active materialand suitable salts include LiPF₆, LiBF₄, LiAsF₆, LiSbF₆, LiClO₄, LiO₂,LiAlCl₄, LiGaCl₄, LiC (SO₂CF₃)₃, LiN (SO₂CF₃)₂, LiSCN, LiO₃SCF₃, LiC₆F₅SO₃, LiO₂CCF₃, LiSO₆F, LiB(C₆H₅)₄, LiCF₃SO₃, and mixtures thereof.

Suitable low viscosity solvents include esters, linear and cyclic ethersand dialkyl carbonates such as tetrahydrofuran (THF), methyl acetate(MA), diglyme, trigylme, tetragylme, dimethyl carbonate (DMC),1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE),1-ethoxy,2-methoxyethane (EME), ethyl methyl carbonate, methyl propylcarbonate, ethyl propyl carbonate, diethyl carbonate, dipropylcarbonate, and mixtures thereof. High permittivity solvents includecyclic carbonates, cyclic esters and cyclic amides such as propylenecarbonate (PC), ethylene carbonate (EC), butylene carbonate,acetonitrile, dimethyl sulfoxide, dimethyl, formamide, dimethylacetamide, γ-valerolactone, γ-butyrolactone (GBL),N-methyl-pyrrolidinone (NMP), and mixtures thereof. The preferredelectrolyte for a Li/SVO or Li/CF_(x) primary cell is 0.8M to 1.5MLiAsF₆ or LiPF₆ dissolved in a 50:50 mixture, by volume, of PC as thepreferred high permittivity solvent and DME as the preferred lowviscosity solvent.

An intermediate ring-shaped pre-form of gold 42 resides between the lid38 and the upper edge 18 of the container sidewall 16. Preferably, theupper annular edge 18 is first metallized with an adhesion layerfollowed by a wetting layer disposed on the adhesion layer. The adhesionlayer is titanium and the wetting layer comprises molybdenum or niobium.

Then, an ultra-sonic weld or laser weld is used to melt and seal thegold 42 to the metal lid 38 and the container sidewall 16, therebyclosing the open end of the container. In particular, the gold 42contacts and seals between the annular edge 18 of the ceramic containersidewall 16 and an inner surface 44 of the lid 38 proximate the lidouter annular edge 40. The gold seal 42 between the lid 38 and thewetting metallization contacting the adhesion metallization contactingthe ceramic sidewall 16 has a leak rate that is not greater than 1×10⁻⁷std. cc He/sec.

With the metal lid 38 sealed to the open end of the ceramic container12, careful control of the stack-up tolerances is important so that thecathode active material 46 physically contacts the inner surface 44 ofthe lid 38. To help ensure intimate and direct contact between the lid38 and the cathode active material, the active material 36 in sheet orplate form is pressed against the inner surface 44 of the lid so thatthe lid “carries” the cathode active material. Alternatively, thecathode material can be spray-coated or printed onto the lid 38 using anorganic binder to adhere the cathode material to the lid. That way, themetal lid 38 is in electrical continuity with the cathode activematerial 36 to thereby serve as the positive terminal for theelectrochemical cell 10. Suitable cathode active materials are selectedfrom LiCoO₂, LiMnO₂, LiMn₂O₄, LiFePO₄, Ag₂V₄O₁₁, V₂O and lithium nickelmanganese cobalt oxide (LiNi_(a)Mn_(b)Co_(1-a-b)O₂).

Further, the anode active material 32 is in electrical continuity withthe anode current collector 30 which is in turn in electrical continuitywith the platinum-containing material 26 or CRMC material 28hermetically sealed to the ceramic base 14 in the anode via hole 20.Outer surfaces of the positive polarity metal lid 38 and the negativepolarity platinum-containing material 26 or the CRMC material 28 areconfigured for electrical connection to a load.

An exemplary chemistry for the miniature primary electrochemical cell 10shown in FIG. 1 has lithium as an anode active material 32 and eithersilver vanadium oxide or fluorinate carbon (CF_(x)) and the cathodeactive material 36. An exemplary chemistry for the miniature secondaryor re-chargeable electrochemical cell 10 shown in FIG. 1 has lithium asan anode active material 32 and LiCoO₂ as a cathode active material 36.In either chemistry, the separator 34 is of polyethylene.

In the exemplary primary electrochemical cell 10, in addition to lithiumas the anode active material 32, the anode can comprise metals capableof alloying with lithium at potentials below 1.0 V vs. lithium such asSn, Si, Al, B, Si—B, and composites of those metals with inactive metalsto reduce volume expansion. The form of the anode may vary, butpreferably it is of a thin sheet or foil that contacts the base 14 ofthe ceramic container 12 and the anode current collector 30.

Broadly, the cathode of a primary cell is of an electrically conductivematerial, preferably a solid material. The solid cathode may comprise ametal element, a metal oxide, a mixed metal oxide, and a metal sulfide,and combinations thereof. A preferred cathode active material 36 isselected from the group consisting of silver vanadium oxide, coppersilver vanadium oxide, manganese dioxide, cobalt nickel, nickel oxide,copper oxide, copper sulfide, iron sulfide, iron disulfide, titaniumdisulfide, copper vanadium oxide, carbon monofluoride, and mixturesthereof.

Before fabrication into an electrode for incorporation into anelectrochemical cell, however, the cathode active material 36 is mixedwith a binder material such as a powdered fluoro-polymer, morepreferably powdered polytetrafluoroethylene or powdered polyvinylidenefluoride (PVDF) present at about 1 to about 5 weight percent of thecathode mixture. Further, up to about 10 weight percent of a conductivediluent is preferably added to the cathode mixture to improveconductivity. Suitable materials for this purpose include acetyleneblack, carbon black and/or graphite or a metallic powder such aspowdered nickel, aluminum, titanium and stainless steel. The preferredcathode active mixture for the electrochemical cell 10 thus includes apowdered fluoro-polymer binder present at about 3 weight percent, aconductive diluent present at about 3 weight percent, and about 94weight percent of the cathode active material.

In the exemplary secondary electrochemical cell 10, in addition tolithium, the anode active materials 32 can comprise a material capableof intercalating and de-intercalating an alkali metal, preferablylithium. A carbonaceous anode comprising any of the various forms ofcarbon (e.g., coke, graphite, acetylene black, carbon black, glassycarbon, etc.), which are capable of reversibly retaining the lithiumspecies, is preferred. Graphite is particularly preferred due to itsrelatively high lithium-retention capacity. Regardless the form of thecarbon, fibers of the carbonaceous material are particularlyadvantageous because they have excellent mechanical properties thatpermit them to be fabricated into rigid electrodes capable ofwithstanding degradation during repeated charge/discharge cycling.

Suitable cathode active materials 36 for the exemplary secondaryelectrochemical cell 10 preferably comprise a lithiated material that isstable in air and readily handled. Examples of such air-stable lithiatedcathode materials include oxides, sulfides, selenides, and tellurides ofsuch metals as vanadium, titanium, chromium, copper, molybdenum,niobium, iron, nickel, cobalt and manganese. The more preferred oxidesinclude LiNiO₂, LiMn₂O₄, LiCoO₂, LiCo_(0.92)Sn_(0.08)O₂,LiCo_(1-x)Ni_(x)O₂, LiFePO₄, LiNi_(x)Mn_(y)Co_(1-x-y)O₂, andLiNi_(x)Co_(y)Al_(1-x-y)O₂.

For the electrochemical cell 10, the lithiated active material ispreferably mixed with a conductive additive selected from acetyleneblack, carbon black, graphite, and powdered metals of nickel, aluminum,titanium and stainless steel. The cathode further comprises afluoro-resin binder, preferably in a powder form, such as PTFE, PVDF,ETFE, polyamides and polyimides, and mixtures thereof.

Nickel is preferred for the anode current collector 30.

In addition to titanium, suitable materials for the lid 38 includestainless steel, mild steel, nickel-plated mild steel, but not limitedthereto, so long as the metallic material is compatible for use with theother cell components.

In an alternate cell design, the cathode active material 36 ispositioned inside the cell casing 12 where the anode active material 32resides in FIG. 1 and the anode active material resides in lieu of thecathode active material. That is, the cathode active material 36 is incontact with the electrically-conductive material 26 or 28 residing inthe via hole 20 and the anode active material is in contact with the lid38.

Thus, the base 14 of the open-ended ceramic container 12 for theelectrochemical cell 10 of the present invention preferably has adiameter that is less 1 cm and the outwardly extending sidewall 16 has aheight that is less than 1 mm. More preferably, total volume for thecell casing comprising the lid 38 sealed to the open end of thecontainer 12 is less than 0.5 cc. Constructing the casing from anopen-ended ceramic container 12 closed by a metal lid 38 enables theminiature electrochemical cell 10 of the present invention. Moreover,the metal lid 38 is sufficiently flexible to accommodate the expecteddimensional changes during discharge of the primary cell and cycling ofthe secondary electrochemical cell.

Now, it is therefore apparent that in an exemplary embodiment thepresent invention relates to a miniature electrochemical cell 10 havinga total volume of less than 0.5 cc. Moreover, while embodiments of thepresent invention have been described in detail, such is forillustration, not limitation.

1. An electrochemical cell, comprising: a) a casing, comprising: i) anopen-ended ceramic container having a via hole extending to a ceramiccontainer inner surface and a spaced apart ceramic container outersurface; ii) an electrically conductive pathway sealed to the ceramiccontainer in the via hole; and iii) a metal lid hermetically closing theopen-ended ceramic container, the lid comprising a lid inner surface;and b) an electrode assembly housed in the casing, the electrodeassembly comprising: i) a first electroactive material contacting theceramic container inner surface and being in an electrically conductiverelationship with the electrically conductive pathway extending throughthe via hole in the ceramic container; ii) an opposite polarity secondelectroactive material contacting the lid inner surface; and iii) aseparator disposed between the first and second electroactive materials;and c) an electrolyte in the casing in contact with the electrodeassembly, d) wherein the electrically conductive pathway serves as afirst terminal, and the lid, electrically isolated from the electricallyconductive pathway by the ceramic container, serves as an oppositepolarity second terminal, and wherein the first and second terminals areconfigured for electrical connection to a load.
 2. The electrochemicalcell of claim 1, wherein the ceramic container is selected from aluminaand 3% YSZ.
 3. The electrochemical cell of claim 1, wherein a currentcollector is supported on the ceramic container inner surface, thecurrent collector being electrically connected to the firstelectroactive material and to the electrically conductive pathwayresiding in the via hole extending through the ceramic container.
 4. Theelectrochemical cell of claim 1, wherein the open-ended ceramiccontainer comprises a ceramic base supporting an outwardly extendingannular ceramic sidewall having an outer annular edge, and wherein theelectrically conductive lid is hermetically secured to the outer annularedge by a gold seal to thereby close the ceramic container.
 5. Theelectrochemical cell of claim 1, wherein the electrically conductivepathway comprises gold.
 6. The electrochemical cell of claim 1, whereinthe electrically conductive pathway comprises a platinum-containingmaterial.
 7. The electrochemical cell of claim 6, wherein theplatinum-containing material is selected from a substantially pureplatinum material and a composite reinforced metal ceramic (CRMC)material, the CRMC material comprising, by weight %, from about 10:90ceramic:platinum to about 90:10 ceramic:platinum.
 8. The electrochemicalcell of claim 7, wherein the CRMC material comprises from about 70:30ceramic:platinum to about 30:70 ceramic:platinum.
 9. The electrochemicalcell of claim 7, wherein the ceramic in the CRMC material is either 3%YSZ or alumina.
 10. The electrochemical cell of claim 1, wherein theelectrode assembly is selected from the group consisting of Li/SVO,Li/CF_(x), Li/LiCoO₂, and Li/LiNi_(a)Mn_(b)Co_(1-a-b)O₂.
 11. Theelectrochemical cell of claim 1, wherein the electrode assembly is ofeither a primary or a secondary chemistry.
 12. The electrochemical cellof claim 1, wherein the lid is selected from the group consisting oftitanium, stainless steel, mild steel and nickel-plated mild steel. 13.An electrochemical cell, comprising: a) a casing, comprising: i) anopen-ended ceramic container comprising a ceramic base supporting anoutwardly extending annular ceramic sidewall having an outer annularedge, the ceramic base having a via hole extending to a ceramic baseinner surface and a spaced apart ceramic base outer surface; ii) anelectrically conductive pathway sealed in the via hole extending throughthe ceramic base of the container; and iii) a metal lid hermeticallysecured to the outer annular edge of the ceramic sidewall by a gold sealto thereby close the open-ended ceramic container, the lid comprising alid inner surface; and b) an electrode assembly housed in the casing,the electrode assembly comprising: i) an anode active materialcontacting the ceramic base inner surface and being in an electricallyconductive relationship with the electrically conductive pathwayextending through the via hole in the ceramic base; ii) a cathode activematerial contacting the lid inner surface; and iii) a separator disposedbetween the first and second electroactive materials; and c) anelectrolyte in the casing in contact with the electrode assembly, d)wherein the electrically conductive pathway serves as a negativeterminal, and the lid, electrically isolated from the electricallyconductive pathway by the ceramic container, serves as a positiveterminal, the negative and positive terminals being configured forelectrical connection to a load.
 14. The electrochemical cell of claim13, wherein the ceramic container is selected from alumina and 3% YSZ.15. The electrochemical cell of claim 13, wherein a current collector issupported on the ceramic container inner surface, the current collectorbeing electrically connected to the first electroactive material and tothe electrically conductive pathway residing in the via hole extendingthrough the ceramic container.
 16. The electrochemical cell of claim 13,wherein the electrically conductive pathway comprises gold.
 17. Theelectrochemical cell of claim 13, wherein the electrically conductivepathway comprises a platinum-containing material selected from asubstantially pure platinum material and a composite reinforced metalceramic (CRMC) material, the CRMC material comprising, by weight %, fromabout 10:90 ceramic:platinum to about 90:10 ceramic:platinum.
 18. Theelectrochemical cell of claim 17, wherein the CRMC material comprisesfrom about 70:30 ceramic:platinum to about 30:70 ceramic:platinum. 19.The electrochemical cell of claim 17, wherein the ceramic in the CRMCmaterial is either 3% YSZ or alumina, and mixtures thereof.
 20. Theelectrochemical cell of claim 13, wherein the electrode assembly isselected from the group consisting of Li/SVO, Li/CF_(x), Li/LiCoO₂, andLi/LiNi_(a)Mn_(b)Co_(1-a-b)O₂.
 21. The electrochemical cell of claim 13,wherein the electrode assembly is of either a primary or a secondarychemistry.
 22. The electrochemical cell of claim 13, wherein the lid isselected from the group consisting of titanium, stainless steel, mildsteel and nickel-plated mild steel.
 23. An electrochemical cell,comprising: a) a casing, comprising: i) an open-ended ceramic containerhaving a via hole extending to a ceramic container inner surface and aspaced apart ceramic container outer surface; ii) a gold pathway sealedto the ceramic container in the via hole; and iii) a metal lidhermetically closing the open-ended ceramic container, the lidcomprising a lid inner surface; and b) an electrode assembly housed inthe casing, the electrode assembly comprising: i) an anode activematerial contacting the ceramic container inner surface and being in anelectrically conductive relationship with the gold pathway extendingthrough the via hole in the ceramic container; ii) a cathode activematerial contacting the lid inner surface; and iii) a separator disposedbetween the anode and cathode active materials; and c) an electrolyte inthe casing in contact with the electrode assembly, d) wherein the goldpathway serves as a negative terminal, and the lid, electricallyisolated from the gold pathway by the ceramic container, serves as apositive terminal, and wherein the negative and positive terminals areconfigured for electrical connection to a load.
 24. A method forproviding an electrochemical cell, comprising the steps of: a) providingan open-ended ceramic container having a via hole extending to a ceramiccontainer inner surface and a spaced apart ceramic container outersurface; b) filling a paste of a platinum-containing material into thevia hole and then heating the ceramic container to transform the pasteinto a platinum-containing material hermetically sealed to the ceramiccontainer in the via hole; c) depositing a current collector onto theinner surface of the ceramic container so that the current collectorcontacts the platinum-containing material; d) positioning a firstelectroactive material on the current collector so that the first activematerial is electrically connected to the platinum-containing materialin the via hole through the current collector; e) positioning aseparator on the first electroactive material; f) positioning a secondelectroactive material on the separator opposite the first electroactivematerial; g) providing an electrolyte in the casing in contact with thefirst and second electroactive materials; and h) securing anelectrically conductive lid to the container to close the open endthereof and thereby provide a casing housing the first and secondelectroactive materials separated from direct physical contact with eachother by the separator, wherein the lid contacts the secondelectroactive material, and i) wherein the electrically conductivepathway contacting the first electroactive material serves as a firstterminal, and the lid, electrically isolated from the electricallyconductive pathway by the ceramic container, contacting the secondelectroactive material serves as a second terminal for the cell, thefirst and second terminals being configured for electrical connection toa load.
 25. The method of claim 24, including providing the open-endedceramic container comprising a ceramic base supporting an outwardlyextending annular sidewall having an outer annular edge, andhermetically sealing the electrically conductive lid to the outerannular edge by a gold seal to thereby close the ceramic container. 26.The method of claim 25, including the gold seal comprising a goldpre-form and melting the gold pre-form using an ultra-sonic weldingprocess or a laser welding process.
 27. The method of claim 25,including, prior to sealing the electrically conductive lid to the outerannular edge of the container sidewall by the gold seal, contacting theouter annular edge of the ceramic container with an adhesion layerfollowed by a wetting layer disposed on the adhesion layer.
 28. Themethod of claim 24, including providing the paste of theplatinum-containing material filled into the via hole in the ceramiccontainer comprising a binder, and subjecting the ceramic container to aheating profile that comprises a binder bake-out heating portion, asinter heating portion, and a cool down portion to thereby transform thepaste into the platinum-containing material hermetically sealed to theceramic container in the via hole.
 29. The method of claim 24, includingproviding the first electroactive material being an anode activematerial and the second electroactive material being a cathode activematerial.
 30. The method of claim 24, including providing the electrodeassembly being of either a primary or a secondary chemistry.
 31. Themethod of claim 24, including depositing a current collector onto theinner surface of the ceramic container using physical vapor deposition(PVD) process.